The process control of fluids in a pumping system has numerous applications, but it is especially useful in the microelectronics industry. However, the slightest contamination within the fluids used in producing microelectronic devices can create defects, decrease production yields, degrade device performance, and reduce device reliability. As a corollary, the pumps that distribute fluid onto the substrates that form such devices have to be able to deliver precise and accurate amounts of fluid. Moreover, the manner in which the fluid is delivered in layers by the pump is critical for producing such devices.
The trend in the microelectronics industry is to squeeze greater quantities of circuitry onto smaller substrates. Circuit geometries have been shrunk to less than one micron. In that microscopic world, the slightest particle of contamination or variations in thickness in the layering of fluid delivered to the substrate can create a defect, decreasing production yields, degrading device performance, and reducing device reliability.
For this and other reasons, modern manufacturing techniques in the microelectronics and other industries sometimes involve decontaminated "cleanroom" environments. Many of these techniques also use so-called advanced process chemicals, some of which are very expensive. For example, certain chemicals used to process semiconductors can cost as much as $15,000 or more per gallon, and the semiconductor substrates can be worth $20,000 or more at that stage or processing.
To be useful in cleanroom environments and applications, however, the chemicals must be filtered and dispensed. Because of the viscosities and sensitivities of the fluids, they must be filtered at low flow rates and under low pressure to minimize molecular shear on the fluids. After the filtration of the process fluids, the process fluid is typically dispensed onto a substrate. Depending on the usage of the substrate, dispensing ability of a pump can be allowed to vary. There is typically a cost efficiency analysis that can be applied to such pumps. For example, certain prior art systems utilize diaphragm-type pumps in which the diaphragm is actuated by air pressure. Typically, the actuating air is more compressible than the liquids being pumped. As air pressure is increased in an attempt to displace the diaphragm and dispense fluid, the actuating air is compressed, in effect "absorbing" part of the intended displacement of the diaphragm. This air compression prevents accurate control and monitoring of the position of the diaphragm and, correspondingly, it prevents accurate control and monitoring of the volume and rate of fluid dispensed.
However, it is clear that an air driven pump that would overcome this problem provides significant advantages. Such pumps are simpler to maintain and less costly than a digitally controlled electro-hydraulic pump, and they are also at least, if not more accurate than a simple pneumatic pump. There is therefore a need in the art to develop an air-driven pump that has greater levels of accuracy and can provide an "intermediate" level of dispense performance.